Clutches for automatic shift gearboxes (ASG), twin-clutch or multi-clutch transmissions (TCT) as well as separable power-divider transmissions and transaxles are constructed as dry or wet clutches. Actuation thereof takes place either electromechanically or hydraulically, wherein hydraulic actuation due to the high power density of the actuators offers advantages with respect to physical arrangement in the transmission. Thus, the clutches can be actuated directly (by so-called ‘central engagers or disengagers’) and additional friction losses due to mechanical motion transmitting mechanisms or the like are avoided. The arrangement in the transmission or between motor and transmission also offers accommodation advantages relative to electromechanical actuation systems, which often protrude beyond the silhouette of the transmission and thus hamper installation of the transmission in the motor vehicle.
Known hydraulic actuation devices (see, for example, DE A-43 09 901, FIG. 1; DE-A-196 37 001, FIG. 27; DE-A-199 50 443, FIG. 11F) usually have a pressure generating unit or pumping and storage unit (so-termed ‘powerpack’), a valve block with several electromagnetically actuable valves for distribution of the hydraulic energy to the individual actuators, lines for conducting fluid, and the actuators or cylinders themselves, optionally with integrated sensor system for positional determination of the setting elements. Activation of the hydraulic actuating device in a multi-clutch transmission for motor vehicles is usually carried out by way of a transmission control unit or a superordinate vehicle computer.
A disadvantage of hydraulic actuating devices of that kind with a storage unit is that the pressure medium, i.e. the hydraulic fluid, for charging of the storage unit has to be pumped to a pressure level far above the maximum required pressure in the actuators in order after removal of the required quantity to still be able to offer the requisite operating pressure, which is disadvantageous in terms of energy and significantly reduces the efficiency of the device. Moreover, the magnetic valves, which are predominantly constructed as slide valves, require a high level of fluid cleanliness due to the closely toleranced gaps and frequently oblige filtering measures. The slide valves employed nevertheless have a not insubstantial amount of leakage, which over a corresponding period of service leads to complete discharging of the storage unit, which has the consequence of delay of the first actuation by the time for charging the storage unit. Also, in the case of driving without changing gear, for example on a motorway, recharging of the storage unit at regular intervals is therefore required, which is equally disadvantageous in terms of energy. Finally, the valve block with the magnetic valves takes up a considerable amount of installation space in the transmission and represents the greatest cost factor within the described actuating device.
What is desired is to provide for the actuation of clutches in, in particular, a multi-clutch transmission for motor vehicles, a hydraulic actuating device which avoids the above disadvantages and by comparison with the outlined prior art has above all a significantly improved overall efficiency with lower costs.